Exhaust mufflers formed at least in part from stamped components have been available for many years. The typical prior art stamped muffler includes at least a pair of stamp formed external shells. These shells include peripheral flanges dimensioned and configured to be placed generally in register with one another. Portions of each shell intermediate the peripheral flanges are formed to define at least one chamber. The prior art stamp formed muffler further includes one or more internal components between the external shells to define a flow path for exhaust gas through the muffler. In some prior art mufflers, the flow path has been defined by an array of conventional tubes. Examples of mufflers of this general type are shown in U.S. Pat. No. 4,901,816 which issued to David Garey on Feb. 20, 1990 and in U.S. Pat. No. 4,905,791 which issued to David Garey on Mar. 6, 1990. These prior art patents are assigned to the assignee of the subject invention. It will be noted that the external shells of the mufflers shown in U.S. Pat. No. 4,901,816 and in U.S. Pat. No. 4,905,791 include baffles formed from the external shells for supporting the conventional tubes within the muffler. Other prior art mufflers have employed conventional tubes supported by separate transverse baffles and disposed within a stamp formed external shell. A muffler of this general type is shown in published U.K. Patent Application No. 2,120,318A.
Many other prior art mufflers include stamp formed external shells and one or more stamped internal plates formed to define the flow path for exhaust gas through the muffler. An extremely effective muffler of this general type is shown in re-issue Pat. No. Re. 33,370 which was re-issued on Oct. 9, 1990. Re-issue Patent No. Re. 33,370 also is assigned to the assignee of the subject invention. It will be noted that Re. 33,370 shows a muffler with a pair of formed internal plates defining an array of tubes through which exhaust gas in the muffler flows. At least one of the tubes defined by the plates is a tuning tube which communicates with a low frequency resonating chamber. The pair of formed internal plates shown in Re. 33,370 is disposed between the pair of external shells that define the chambers of the muffler.
Other patents assigned to the assignee of the subject invention show still other advances in stamp formed exhaust mufflers. For example, U.S. Pat. No. 4,860,853 which issued to Walter G. Moring, III on Aug. 29, 1989 shows a muffler that can be formed with only three stamped components, but still defining an efficient flow path for exhaust gases and a plurality of chambers for attenuating the noise associated with the flowing exhaust gases. U.S. Pat. No. 4,894,987 issued to Jon Harwood et. al. on Jan. 23, 1990 and covers a stamp formed muffler and catalytic converter assembly.
A vehicular exhaust system generally must travel an extremely circuitous route from one end of the vehicle to the other, and the various components of the exhaust system often must be disposed in closely nested relationship to other parts of the vehicle. Components of the exhaust system, including the muffler, become very hot when the vehicle is operating due to the flow of heated exhaust gas therethrough. In many situations, it is necessary to employ a shield in proximity to the muffler or some other component of the vehicular exhaust system. The shield generally is slightly spaced from the heated exhaust system component and hence provides an insulating layer of air between the shield and the hot exhaust system component. In some situations, the shield is disposed on the side of the muffler or pipe facing away from the vehicle to prevent the heated exhaust system component from igniting dried leaves or grass near the vehicle. Hence, shields mounted on the side away from the vehicle may be referred to as grass shields. In many other situations, the shield is disposed between the muffler or pipe and the vehicle to prevent overheating of floor boards or other parts of the vehicle disposed near the exhaust system component. Shields mounted between the exhaust component and the vehicle generally are referred to as heat shields. The term heat shield will be used herein to refer to any shield regardless of its orientation on the muffler.
The prior art heat shield for an exhaust system component generally has been a flat or slightly curved piece of sheet metal that is strapped to the muffler or pipe. The heat shield may further be formed with stand-offs to achieve the desired spacing from the exhaust system component An extremely effective heat shield of this general type is shown in U.S. Pat. No. 4,478,310 which issued to Donald Harter on Oct. 23, 1984 and which is assigned to the assignee of the subject invention.
Heat shields may be stamp formed efficiently and employed with stamp formed mufflers For example, a heat shielded stamped formed exhaust muffler is shown in U.S. Pat. No. 4,759,423 which issued to Harwood et. al. on Jul. 26, 1988 and which also is assigned to the assignee of the subject invention. The muffler shown in U.S. Pat. No. 4,759,423 employs a pair of stamped internal plates and a pair of stamped external shells to achieve a tri-flow pattern of exhaust gas which in many respects resembles the flow pattern formed with conventional mufflers One embodiment of the muffler shown in U.S. Pat. No. 4,759,423 further employs a heat shield generally conforming to the shape of one of the external shells to nest over the external shell for attachment around the periphery of the muffler. This design provides extremely effective heat shielding. However, the welding or mechanical attachment of five thicknesses of metal around the periphery of the muffler can be difficult. Additionally, the heat shield will not become as hot as the muffler and hence will expand and contract differently. This differential expansion and contraction can damage the welded connection of the heat shield to the muffler. Furthermore, the heat shield often will perform its shielding function if formed from a thinner grade of metal. However, thinner metal is easily damaged by the heat of welding. Thus, it has been necessary to make the heat shield from a thicker metal and thereby incur a cost and weight penalty. As an alternative to the welding or mechanical attachment around the periphery of the muffler, straps could be employed as in the above referenced U.S. Pat. No. 4,478,310. However, straps require additional material, additional weight and an assembly process that is not well suited to automation.
FIGS. 1 and 2 show a prior art stamp formed external shell for an exhaust muffler. The prior art external shell shown in FIGS. 1 and 2 is identified generally by the numeral 10, and is stamped from an initially rectangular flat sheet of metal. A peripheral flange 12 generally will retain its initial planar configuration. However, a central region of the external shell 10 is formed to define at least one chamber 14 The prior art external shell 10 typically will be formed in a progressive stamping die wherein the initially planar rectangular sheet is sequentially worked into the shape of the external shell 10 depicted in FIGS. 1 and 2. As part of this formation process, the metal material of the external shell 10 will deform and stretch to enable the formation of the chamber 14. As shown most clearly in FIG. 2, the external shell 10 will achieve a non-rectangular peripheral configuration due to the stretching and deformation of the metal. In particular, portions of the metal intermediate the corners will be drawn inwardly to enable the formation of the chamber 14. A final step of the progressive stamping operation typically will be to cut the peripheral flange 12 of the external shell 10 into a uniform width as shown by the edge 16 in FIG. 2, which, in this instance is rectangular. Metallic material disposed outwardly from the final edge shape 16 will be accumulated and resold for scrap. However, there is a substantial loss in value in the metal material sold for scrap.
Although the above described stamped mufflers and heat shields are extremely effective, it is desired to provide further efficiencies and improvements in the manufacture of heat shielded mufflers. As a result, it is an object of the subject invention to provide a more efficient heat shield and exhaust muffler combination.
It is another object of the subject invention to provide efficient methods for manufacturing and assembling a heat shielded exhaust muffler.
It is still another object of the subject invention to provide a muffler and heat shield combination with an efficient attachment between the muffler and the heat shield.
Still an additional object of the subject invention is to provide a muffler and heat shield assembly with an efficient means for achieving a desired stand-off therebetween